Atrial fibrillation is a condition wherein the upper chambers of the heart, called the atria, flutter or quiver rapidly. By some estimates, 1 in 20 people over the age of 65 experience atrial fibrillation. During atrial fibrillation, the contractions of the atria are not coordinated with the contractions of the ventricles. This can result in improper filling of the ventricles and inefficient operation of the heart. Individuals suffering from atrial fibrillation may experience palpitations, dizziness, fainting, weakness, fatigue, shortness of breath, and angina. In addition to causing discomfort for patients and potentially limiting physical activity, atrial fibrillation can cause very serious complications. For example, atrial fibrillation allows blood to stagnate inside of the heart, which can lead to the formation of blood clots. Blood clots in the vasculature are dangerous and can result in substantial morbidity and mortality. For example, a blood clot can result in a myocardial infarction if lodged in the coronary artery or a stroke if lodged in an artery that supplies blood to the brain. Blood clots that follow from atrial fibrillation are believed to account of at least one-third of stroke incidence in patients over 85 years of age. For these reasons, is important to provide effective medical treatment for atrial fibrillation.
Various therapeutic approaches currently exist for treating atrial fibrillation, including the administration of drugs for ventricular rate control and drugs for atrial rhythm control. Such drugs can include digoxin, beta adrenoceptor blockers (such as atenolol, metoprolol, and propranolol), amiodarone, disopyramide, calcium channel antagonists (verapamil, diltiazam), sotalol, flecainide, procainamide, quinidine, and propafenone, among others. However, the use of drugs is not always effective and can result in undesirable side effects.
Another approach for treating atrial fibrillation involves the ablation of tissues on or near the heart. Ablation is a process of physically destroying tissue. Ablation of tissue prevents the destroyed tissue from initiating and/or conveying inappropriate excitatory depolarization waves. Ablation techniques to control atrial fibrillation generally involve applying radiofrequency (RF), microwave, ultrasound, laser, or other energy to certain tissue, or by freezing (usually through a catheter) certain tissue on or near the heart. Ablation results in a small scar that is electrically inactive and incapable of generating or propagating inappropriate electrical signals. The electrical abnormalities associated with atrial fibrillation are often generalized across the tissue of the atria. Therefore, control of atrial fibrillation through ablation often includes forming a series of scars across the atria, rather than just in one localized area. Techniques such as the MiniMaze or Cox Maze procedures involve creating a pattern of atrial lesions or scars to control the propagation of inappropriate electrical signals.
However, there are significant drawbacks associated with tissue ablation. One drawback is that ablation can be a lengthy procedure and exposes the patient to a risk of stroke. There is also a risk of causing unintentional damage to surrounding tissue during an ablation procedure. Finally, tissue ablation is non-reversible, and the long-term side-effects are poorly understood.
Improved methods for treating atrial fibrillation and related devices are needed.